1. Field of the Invention
The present invention relates generally to a method for backward reproduction in a time-lapse video tape recorder. More specifically, the present invention relates to a method for backward reproduction a in time-lapse video tape recorder for reviewing images of good quality from a previously recorded video signal frame by frame only with a simple servo control. The present backward reproduction method stores temporally video signals, which are reproduced while a magnetic tape is moved forward, in a memory and reading out them in a reverse order in which they have been stored.
2. Brief Description of the Related Art
Unlike an ordinary continuous video tape recorder which records every frame of video signals, a time-lapse video tape recorder intermittently records video signals from several video cameras or the like on a magnetic video tape with a pre-selected regular interval while the recorder repeats running and stopping of the tape. Such a device has been useful in various security sensitive places, e.g., banks and museums, because these places require long-time recording of several sites for security monitoring. As shown in FIG. 1, a conventional time-lapse video tape recorder comprises an A/D converter 100 streams, a buffer memory 201 in which the digital video data are stored temporarily; a field memory 202 in which the digital video data from the buffer memory 201 are stored before they are recorded, a D/A converter 300 which converts the digital video data stored in the field memory 202 into an analog video signal, a recording/reproduction unit 400 which records the analog video signal on the magnetic tape, and a controller 500 which controls writing/reading intervals of video signals from the external video cameras to/from memories 201 and 202 according to the instruction input through an input unit 600 from a user.
The recording/reproduction unit 400 comprises a video signal processing unit and mechanical elements, shown in FIGS. 1 and 2, such as a loading motor 401 which moves a loading post 1 to load/unload the magnetic tape 10; a drum motor 402 which rotates a head drum 3 on which video heads 2 are mounted to record/reproduce video signals on/from the magnetic tape 10; a capstan motor 403 which rotates a capstan shaft 4 to drive the magnetic tape 10 at a designated tape running speed.
In a conventional time-lapse video tape recorder configured as above, one frame is extracted from a continuous video signal that is received from an selected external video camera at a predetermined interval and is then stored temporarily in the buffer memory 202 via the A/D converter 100. Then, the video frames in the buffer memory 202 are transferred into the field memory 202. This way, a continuous video signal is compressed in time domain. The time compressed signal is a digital video signal which is sub-sampled by frame.
When the field memory 202 becomes fill with the extracted video frames, they are read out at a time under the control of the controller 500 and are then converted into an analog video signal by the D/A converter 300. Then, the analog video signal begins to be recorded on the tape 10 immediately after reloading the tape 10 that has been unloaded during a recording pause period in which no video signal is recorded.
While the video frames in the field memory 202 are recorded on the tape 10, new video frames are sampled intermittently from a continuous video signal received from the external video camera and stored in the buffer memory 201 temporarily. As soon as the recording of the video frames in the field memory 202 is completed, the video frames, which have been stored in the buffer memory 201 for the recording operation, are transferred to the field memory 202, along with video frames which are newly stored in the buffer memory 201 after the completion of the recording operation. Whether or not the video frames are to be stored in the buffer memory 201 after the completion of recording operation depends on the storage capacity of the buffer memory 201.
After recording the video frames intermittently as above, when a user inputs a backward reproduction instruction to review the video signal previously recorded on the tape 10 in a reverse order, the video signal is reproduced in the reverse direction, field by field (or frame by frame), based on a control pulse (e.g., a pulse signal of 30 Hz) recorded in a control track along a lower part of the tape 10, as shown FIG. 3, while the tape 10 is being moved backward by the capstan motor 403.
In the explained conventional method for backward reproduction, however, because control pulses are read out during the reverse movement of the tape, the detected level of the control pulses decreases so that a complex servo control is needed to accurately reverse the tape one by one field (or one by one frame). Moreover, since the control pulses are recorded on the lower line track of the tape, if a little distortion of the tape occurs during the reverse movement, it is difficult to extract the control signal accurately, leading to difficulty in precisely locating each of video tracks on the tape during the time of backward reproduction, and control noise and beat noise may lower the quality of the reproduced video signal.
Accordingly, an object of the present invention is to solve the above mentioned problems and other problems of conventional methods and to provide a method for backward reproduction in a time-lapse video tape recorder that makes it possible to review in reverse the high-quality video signal that was previously recorded on a magnetic tape field by field (or frame by frame) through a simple servo control.
According to the present invention, a method for backward reproduction in a video tape recorder having a memory, includes the steps of identifying a current position of a tape; moving the tape in reverse for a predetermined distance from the identified position; reproducing a video signal recorded on the tape while moving the tape in the forward direction after the moving step; storing the reproduced video signal in the memory of a recording device in digital form according to a storage order; and retrieving digital video data stored in the memory in a reverse order of the storage order.
Further, a method for backward reproducing video information recorded on a recording medium, according to the present invention includes the steps of first moving a recording tape in a backward direction from a current position for a predetermined distance; second moving the recording tape in a forward direction after the first moving step; reproducing video signals from the recording tape during the second moving step; storing a digital form of the reproduced signals in a memory of a reproduction apparatus according to a storage order; and outputting the stored digital signals from the memory according to a reverse order of the storage order.
In the method for backward reproduction according to the present invention, when the backward reproduction instruction is entered by a user, instead of just reproducing recorded video signal while moving the tape in reverse, the position of the tape at which the video head is contacting at that time is determined by reading the position identification number that has been superimposed within a particular period of the video signal and then has been recorded on the tape. Then, the tape is moved in the backward direction by an amount, which is dependent on the storage capacity of the memory. After that, while running the tape in the forward direction, the video signal is reproduced and stored in the memory through digitization. Thus, the backward reproduction of the previously recorded video signal is done by reading out and reproducing the video signal from the memory in the reverse order in which it has been stored.
Unlike the conventional method for backward reproducing of video signal based on control signal on the tape, because the method according to the present invention retrieves digital video signal that has been reproduced while the tape moves in the forward direction, it offers better quality of video images and requires less complex servo control than the conventional method. Furthermore, it enables us to review images of good quality in backward reproducing mode without control noise or beat noise from the previously recorded video signal field by field (or frame by frame).
The above objectives, features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof to read in conjunction with the accompanying drawings.